Currently the only way to build a workflow validator that checks against the values of Assets custom fields is using Jira Expressions. With Jira Expressions, the Assets custom field provides only the object IDs of the Assets objects stored in that field. It would be helpful to be able to know specific attributes on the object, or whether the object matches a given AQL, in order to make more powerful workflow validators.

This ticket explicitly doesn't recommend a specific approach to fix this, as there are a few ways that this could be solved:

• A new workflow validator specific to Assets custom fields, built into Jira, that checks whether the values in a given Assets custom field match some AQL query.
• New methods in Jira Expressions that allow us to check whether Assets field values match a given AQL, e.g. something like this could work:

  issue.fieldMatchesAql('customfield_12345', 'Label like a')

• Providing full access to the Assets object attributes during a Jira Expression so that it can be queried directly, e.g. 

  issue.customfield_12345[0].label = "blah"

• or perhaps some other approach (feel free to leave a suggestion in the comments).